The present invention relates to a method of manipulating sheets, especially printed sheets. More particularly, the invention relates to improvements in a method of assembling different types of sheets into groups, such as newspapers wherein a folded-over outer section confines one or more inner sections or inserts each of which, in turn, can constitute a folded-over section. Still more particularly, the invention relates to improvements in a method of stacking or interleaving two or more differently dimensioned, imprinted and/or colored sheets to form groups of dissimilar sheets, newspapers with one or more sections inserted into an outer section, and/or a combination of these.
U.S. Pat. No. 3,414,257 and Swiss Pat. No. 449,666 disclose a machine for the transport of first sheets along a single elongated path and for addition of one or more second sheets to successive first sheets in such path. Each first sheet is delivered into the receiving or inlet end of a channel which defines the elongated path, and the first sheets are transported along such path to advance past one or more locations of admission of second sheets. If the first sheets are folded over themselves, they can be opened up prior to reaching the location for reception of the foremost or another second sheet so that each second sheet or any selected second sheet can be inserted into the space between the spread-apart panels of the oncoming first sheet. Such procedure can be followed, for example, to assemble the sections of newspapers wherein an outer section confines one or more additional sections or inserts.
A drawback of the just described conventional machines and of the method which can be practiced by resorting to such machines is that the output is relatively low. This is due to the fact that the rate at which the first and second sheets can be transported along the single elongated path during assembly of each first sheet with one or more second sheets is well below the maximum output of feeding units or feeders which deliver sheets into the path. Thus, and in order to allow for proper assembly of first and second sheets, the feeding units which deliver first and second sheets into the aforementioned path must be operated well below capacity. The speed of transport of sheets along the elongated path cannot be increased at will because the sheets would be likely to undergo deformation in response to contact with pushers which advance the sheets along the path as well as owing to resistance of air and the development of air currents as a result of rapid advancement of the sheets. On the other hand, the just discussed method of assembling first and second sheets exhibits many important advantages, especially because it can be practiced by resorting to relatively simple, compact and reliable machines. Moreover, the initial and maintenance costs of the machines are very reasonable, and the extent to which such machines must be attended to or monitored in actual use is negligible.